The present invention relates to rotary gear pumps, and in particular to improved rotary gear pumps which may readily be flushed of pumped material.
Color change systems for spray coating apparatus have particular application in industrial operations where articles or ware are to be spray coated at a spray station, or are to be coated as they move along a production line. Where the articles are required to be coated a wide variety of colors, it is generally not practical to establish separate spray stations or production lines for each color, or even to spray a long sequence of articles of one color, then another long sequence of articles of a second color, etc. Instead, it is desirable to be able to make color changes rapidly and simply at a single spray station.
Color change systems are useful in such cases, and provide for a variety of colors to be sprayed from a single spray gun. With many conventional systems, a plurality of supply containers of fluid, each of a different color and having a separate motor driven transfer pump or a source of pressurization for the container, are connected with a manifold through valve controlled ports. An outlet from the manifold connects with an inlet to the spray gun, and to spray material of a particular color the port valve associated therewith is opened to provide the fluid through the manifold to the gun. After completion of spraying coating material of a particular color, the manifold and gun are flushed with a flushing media of solvent and compressed air to clean the system in preparation for spraying material of a different color.
Although the foregoing types of color change systems provide versatility in spraying a plurality of different colored fluids with a single spray gun, requisite manifold flushing between color changes imposes time limitations on the color change process, which limitations become significant in use of high solids paints which do not flush rapidly. Consequently, such systems lack versatility for use with production lines in which rapid color changes are necessary.
In many spray coating applications it is necessary that the quantities of coating materials supplied to the spraying equipment be accurately metered or dosed, thereby to supply a specified amount of material to be applied on an article or, in the case of plural component systems, to maintain accurate ratios between the quantities of different material combined in a spray. For the purpose, rotary gear metering pumps are often used as part of or at the outlet from a color changer to deliver coating material to spray coating equipment.
Although rotary gear pumps are well suited for delivering metered quantities of coating material to spray coating apparatus, a difficulty arises in their use with color change equipment. Since the coating material passes through the pump, to change from spraying material of one color to spraying material of another, the pump must first be thoroughly cleansed to prevent contamination of coating material colors. Because of the particular structure of conventional rotary gear pumps, significant time delays are encountered in cleansing the same between color changes.